World's most polluted cities

Severe pollution is once again choking Shanghai and other cities in China, disrupting hundreds of flights and forcing schools to close. China is home to some of the world's most polluted cities -- take a look at some of the others.

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Sumgayit, Azerbaijan -- Another industrial center for the Soviet Union, Sumgayit was home to more than 40 factories producing industrial and agricultural chemicals like detergents and pesticides. Most of the factories have been shut down, but the effects remain. Today cancer rates are 22 to 51 percent higher than the national average, while cancer mortality rates are 8 percent higher.